1. Field of the Invention
This invention concerns a lead frame, a semiconductor device manufactured by using the lead frame, and a method for manufacturing the semiconductor device.
2. Description of the Prior Art
Recently, the demand for high integration of semiconductor devices has increased. On the other hand, there is also a demand for reduction of the external dimensions of the semiconductor device after sealing. Since the semiconductor chip size is becoming larger to meet the demand for high integration, the reduction of the external dimensions is very difficult. Many efforts have been made to reduce the external dimensions.
FIGS. 1A to 1E show a conventional lead frame and a semiconductor device produced by using the lead frame, shown in Japanese laid open Patent (Tokkai Sho) No: 52-127756. In the prior art, two metalic frame bodies 10 and 20 are used. The first metalic frame body 10 includes a die pad portion 13 and tie bars 12 connecting the die pad portion 13 to a joining band 11. FIG. 1C is a cross sectional view along the line A-A' of FIG. 1B. The second metalic frame body 20 has projecting portions 23 and a plurality of leads 25 extending from a lead connecting portion 24 to the central portion. A dam bar portion 22 supports the leads 25 (FIG. 1B, FIG. 1C). A semiconductor chip 15 is mounted on the die pad portion 13. (FIG. 1D)
The die pad portion 13 is separated from the joining band 11 by cutting along the line B-B'. The die pad portion 13 having the semiconductor chip 15 is welded to the projecting portion 23, and is fixed to the second frame body 20. (FIG. 1E)
Bonding pads (not shown) on the semiconductor chip 15 are electrically connected to the inner lead portions of the leads 25 by bonding wires (not shown).
Since the inner lead portions of the leads 25 overlap the semiconductor chip 15, it is possible to reduce the external dimensions of the semiconductor device as compared to devices wherein the die pad portion and the leads are produced from a single frame body.
However, in the prior art, the die pad portion 13 is separated from the joining band after the semiconductor chip is mounted thereon. Thus, there is a problem of dust adhering to the semiconductor chip during the separation process. Furthermore, there is a problem in handling the frame bodies due to the projecting portions 23, since the projecting portions 23 serve as hooks when the frame bodies are piled up during the manufacturing process.